Steam reforming is a well known method for generating hydrogen from light hydrocarbonn feeds and is carried out by supplying heat to a mixture of steam and a hydrocarbon feed while contacting the mixture with a suitable catalyst, usually nickel. The steam reforming reaction may be represented as: EQU H.sub.2 O+C.sub.x H.sub.y =CO+H.sub.2
with the following equilibria tending to become established EQU CO+H.sub.2 O=CO.sub.2 +H.sub.2 EQU CO+3H.sub.2 =CH.sub.4 +H.sub.2 O
so that the overall reaction, which is endothermic, may be summarized as: EQU H.sub.2 O+C.sub.x H.sub.y =CO+CO.sub.2 +H.sub.2
Steam reforming is generally limited to paraffinic naphtha and lighter feeds which have been de-sulfurized and treated to remove nitrogen compounds, because of difficulties in attempting to steam reform heavier hydrocarbons and the poisoning of steam reforming catalysts by sulfur and nitrogen compounds. Thus economical methods have been needed to convert heavier feeds to hydrogen-rich gases which are suitable for steam reforming.
Another known method of obtaining hydrogen from a hydrocarbon feed is the partial oxidation process in which the feed is introduced into an oxidation zone maintained in a fuel rich mode so that only a portion of the feed is oxidized. The partial oxidation reaction may be represented as: EQU C.sub.x H.sub.y +O.sub.2 =CO+H.sub.2
Steam may also be injected into the partial oxidation reactor vessel to react with the feed and with products of the partial oxidation reaction. The process is not catalytic and requires high temperatures to carry the reactions to completion, resulting in a relatively high oxygen consumption. On the other hand, the partial oxidation process has the advantage that it is able to readily handle hydrocarbon liquids heavier than paraffinic naphthas and can even utilize coal as the source of the hydrocarbon feed.
Catalytic autothermal reforming of hydrocarbon liquids is also known in the art, as evidenced by a paper Catalytic Autothermal Reforming of Hydrocarbon Liquids by Maria Flytzani-Stephanopoulos and Gerald E. Voecks, presented at the American Institute of Chemical Engineers'90th National Meeting, Houston, Texas, April 5-9, 1981. Autothermal reforming is defined therein as the utilization of catalytic partial oxidation in the presence of added steam, which is said to increase the hydrogen yield because of simultaneous (with the catalytic partial oxidation) steam reforming being attained. The paper discloses utilization of a particulate bed of nickel catalyst into which steam, air and a hydrocarbon fuel supply comprising a No. 2 fuel oil are injected to produce a gas containing hydrogen and carbon oxides.
In Brennstoff-Chemie 46, No. 4, p. 23 (1965), a German publication, Von P. Schmulder describes a Badische Anilin and Soda Fabrik (BASF) process for autothermal reforming of gasoline. The process utilizes a first, pelletized, i.e., particulate, platinum catalyst zone followed by a second, pelletized nickel catalyst zone. A portion of the product gas is recycled to the process.
Disclosure of the utilization of a noble metal catalyzed monolith to carry out a catalytic partial oxidation to convert more than half of the hydrocarbon feed stock upstream of a stream reforming zone is disclosed in an abstract entitled "Evaluation of Steam Reforming Catalysts for use in the Auto-Thermal Reforming of Hydrocarbon Feed Stocks" by R. M. Yarrington. I. R. Feins, and H. S. Hwang (National Fuel Cell Seminar, San Diego, July 14-16, 1980.) The paper noted the unique ability of rhodium to steam reform light olefins with little coke formation and noted that results were obtained for a series of platinum-rhodium catalysts with various ratios of platinum to total metal in which the total metal content was held constant.
U.S. Pat. No. 4,054,407, assigned to the assignee of this application, discloses two-stage catalytic combustion platinum group metal catalytic components dispersed on a monolithic body. At least the stoichiometric amount of air is supplied over the stages and steam is not employed.
U.S. Pat. No. 3,481,722, assigned to the assignee of this application, discloses a two-stage process for steam reforming normally liquid hydrocarbons using a platinum group metal catalyst in the first stage. Steam and hydrogen, the latter of which may be obtained by partially cracking the hydrocarbon feed, are combined with the feed to the process.
The catalytic partial oxidation process of the present invention provides a highly efficient method for producing hydrogen-rich gases from hydrocarbons which attains excellent yields in a relatively compact and simple apparatus. These hydrogen-rich gases produced are particularly suitable for steam reforming as compared to the feed to the catalytic partial oxidation unit.